The present invention relates to improvements in a small-sized optical fiber gyroscope wherein a distance, an azimuth, etc., are detected by utilizing an optical interference, and a navigation system wherein the optical fiber gyroscope is employed.
Heretofore, an optical fiber gyroscope which utilizes an optical interference for detecting an azimuth from the change of a rotating angular velocity has had its measurement based on the interference of two light waves which propagate in directions reverse to each other through an optical fiber loop. In other words, the rotating angular velocity is found by measuring the phase difference of interference light which is developed by rotations.
In measuring the phase difference by means of the optical fiber gyroscope in this manner, a phase bias needs to be given beforehand. As an expedient for affording the phase bias, there has been known a technique wherein, as stated in the official gazette of Japanese Patent Application Laid-open No. 135912/1983 or "Applied Optics", 20, (1981) pp. 4313-4318, the two light waves to form the interference light are once guided to separate optical paths and passed through phase plates in the optical fiber gyroscope, thereby to be endowed with the predetermined phase bias. Besides, for enhancing the detection accuracy of the optical fiber gyroscope, it is necessary to consider the influence of feedback light, the compensation of a drift attendant upon any change in the environment of the gyroscope, etc. In these regards, there have been known techniques disclosed in the official gazettes of Japanese Patent Applications Laid-open No. 94680/1981, No. 228113/1984, No. 134513/1990, etc.